Your 15yo with similarly aged siblings? Or a separate 15yo with four much younger not related children?In my experience, no to the first (because siblings fight and wind each other up and there are all sorts of power play issues with who is ‘in charge’, and yes to the second. At 15 I was babysitting for 5 kids and answering the phones for the parents taxi service. At 15 dd1 was standard first aid qualified and paid to work at a pool, at 16 she was lifeguarding.The only issue I have is when the sitter is a sibling.

I would as long as you were nearby and the 15YO could call you and you’d be home in max 10 mins in case one of the younger ones woke up and wouldn’t settle. And maybe consider asking a sensible friend to join just in case?

Me and my brother used to look after my youngest sister when parents went out of a Friday eve... Think I was 13 or 14 when it started, so he was 15ish and she was 4 or 5. Not in bed though... I do remember some rows when we stopped her having a third packet of crisps! Definitely it responsible leave them, it's if he's happy with it i suppose. Will he have to out then to bed? Because they night decide to play up and challenge authority, that's what my sister did, so it could be exhausting for him!

That is fine - my DD15 has her own "babysitting business" - weekends only - she gets £7.50 an hour (!?!?!) and now has 4 clients. Some have good sleepers, some less so... she always says to parents that she is happy to babysit for kids who won't stay abed so long as they are happy to come home to them sitting on the sofa watching telly... so far so good.